


Behind the Scenes

by orphan_account



Category: Undertale (Video Game)
Genre: M/M, Masturbation, Mutual Pining, Unresolved Sexual Tension, Voyeurism, slight almost jealousy?
Language: English
Status: Completed
Published: 2015-11-21
Updated: 2015-11-21
Packaged: 2018-05-02 16:11:52
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,430
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5254820
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>(Takes place post neutral ending in which Mettaton is the only survivor and Sans becomes his agent.)</p><p>It's well after hours when Sans accidentally overhears something he shouldn't, and stays when he really should leave.</p>
            </blockquote>





	Behind the Scenes

**Author's Note:**

> This was barely edited and more or less a speed-write; please forgive me for any mistakes. I hope you can enjoy it, regardless.

One 'shortcut' through the alley beside MTT Resort later and Sans waltzed into the Green Room as though he'd just gone on in through the wall. It was darker in here than he'd expected. A snap of his fingers had a small lick of monster fire curling up over his thumb and forefinger to aid the problem. He held it up as he made his way toward the dressing rooms.

It was well after the show. Upon receiving a compliment on his 'lovely black peacoat' over at Grillbys, Sans had come to the startling realization that he'd left his favorite hoodie backstage. For, you see, he refused to wear anything more flashy than said coat and some matching black pants when on the job with Mettaton. Adorned with gold glitter, it wasn't like they were inconspicuous, besides. He would've teleported all the way there if he knew the strain of it wouldn't knock him out cold for a good three hours. He took the boat and walked most of the way back, instead. A good couple of hours shaved off his free time and precious sleep.

One might wonder how, in his mind, this could have possibly been worth it. After everything that had happened any sense of familiarity was worth clinging to with a vice-like death grip. Even something as simple as a sweatshirt. He wouldn't let it go if he didn't  _have_  to.

He rounded the corner and paused at the sight of a cracked door and a yellow light spilling from within. It was Mettaton's personal dressing room. Sans had been in there enough times to know it was more of a personal little  _penthouse_ than a dressing room. The idea that the robot might stay overnight there didn't surprise him one bit.

Welp, Sans saw no reason not to pop in and say  _'hi'._

He shook the monster fire from his fingers and headed over. Plunged in darkness he was all but a shadow, creeping in unnatural silence. White pinprick eyes glowed eerily alone in a sea of darkness, until he slipped within the light's arc. Reaching out a hand he touched the door, but an odd sound from within stopped him dead.

He wasn't immediately sure why his first instinct was to freeze. He didn't quite comprehend what he'd just heard. Not at first. Not until he found himself stuck there in a shocked daze for several long, agonizing seconds, just  _listening_  to his boss writhe and moan in what must have been absolute ecstasy behind that door.

Sans' magic twisted nauseatingly beneath his ribs, something else  _ice-cold_  cascading down his spine.  _Oh, god,_   _somebody else was in there with him, weren't they?_  Even if the lucky bastard was being awfully quiet right now. It wasn't like Mettaton had any shortage of groupies to cart backstage. It was only a matter of time before this happened, but knowing that didn't make it any less disturbing.

Withdrawing from the door Sans leaned his shoulder against the wall to listen. His eyes narrowed, dimming as Mettaton's vocalizations became muffled. All he could hear now were quiet gasps. He listened for another voice, another's ragged breathing, even, but nothing came.

Curiosity got the better of him. With extreme deliberation he leaned over to peer around the doorframe.

Against all odds Mettaton was alone. He was sprawled out over the couch like a glittering piece of artwork. One hand was between his thighs while the other clutched some blue fabric against his face. Sans found himself riveted even though every logical part of him was screaming for him to look away. Before his eyes Mettaton arched upon the couch with a choked cry of pleasure. He said something, but it was muffled by the cloth over his mouth.

Sans felt his eye start to burn as he watched. Magical energy crackled hot down his spine to pool within his loins, infusing the rest of his body with heat. All those suppressed feelings concerning his boss crashed through him unbidden and he stood no hope of reigning them back in again. All he could do was stare helplessly.

Mettaton moaned something again. He writhed with astounding grace, upper body half slipping off the couch as he parted his legs wider. One lifted, heel resting upon the sofa's back. Little lightning bolts flashed within the soul container on his abdomen, catching Sans' eye. The heart within glowed like a neon sign. In an insane moment of clarity he wondered if that was healthy, mentally scanning through what he'd read of Alphys' notes. Mettaton's voice rang out again and ripped him right from his reverie. This time he heard him loud and clear.

"Oh,  _Sans…"_

His own name, spoken with such breathless need, hit him like a spear straight through the chest. It was at that exact moment he recognized what Mettaton was clutching against his face. The very object he'd come here to retrieve; his hoodie.

Sans whirled away as though struck in the face. His back collided with the wall, hand clasped over his mouth. His eyes were wide though only his left iris was visible; burning blue and flashing. A part of him screamed for him to run. He wanted to leave this impossible situation behind. He wanted to  _forget it ever happened,_ but he was paralyzed.

The logistics of the situation filed through his mind unbidden. He wondered just  _what_ scents Mettaton could be picking up on his sweatshirt right now. The robot's olfactory receptors were fine-tuned to a high degree, likely because that was what Alphys herself considered 'normal'.

Whatever the verdict, he seemed to be enjoying it  _immensely_  if those sounds were anything to go by.

Sans squeezed his eyes shut at the thought and shifted, unable to ignore the burning hot tension between his legs anymore. He didn't think he'd ever been this aroused before in his life. It actually  _ached,_  straining against his shorts and twitching in a way that made him want to grab it. But he refused to touch himself. The fact he was still just  _standing here listening_  was shameful enough.

Again he heard his name, breathless and reverent. The sound tugged at his soul like a serrated fishhook. He couldn't help but wonder  _why._   _Why him, of all monsters?_  Mettaton could have just about  _anybody_  in the Underground, and yet here he was, alone and fantasizing about  _Sans?_ His lazy, utterly devoid-of-a-fashion-sense agent?

Sans' spine scraped against the wall as he sank to the floor under the weight of his own thoughts. Spreading his legs wide the taut fabric of his shorts created some relieving pressure. Both hands covered his mouth as he began lightly rocking, desperate for friction.

The action inside the room behind him seemed to be escalating. Mettaton's voice grew louder and more insistent with rising urgency. Sans felt his own desperation increase tenfold right along with.

He didn't need to open his eyes to know just how  _hard_  he was. He could feel his cock ceaselessly throbbing against the silky fabric of his shorts. He writhed as a tingling numbness began to build, driving him into a frenzy he refused to give in to. He arched his hips up, breath coming sharp and quick, whole body trembling with ravenous, subdued  _need._

With Mettaton's melodious cries to urge him on he didn't last long. Much to his mortification the tension burst suddenly and without warning. Eyes snapping open in shock he started to come, breath catching behind his palm as his other hand shot between his legs. He arched, painfully tense as wave after wave of ecstasy crashed through him. His one visible eye rolled back. He kept his hand clamped tight over his mouth as he struggled to ride it out without making a sound.

When at last it was over he fell back limp and panting in a post-orgasmic daze. His shorts were soaked, his whole body was damp with sweat. He looked at his hands and watched them tremble as he listened to the action in the room behind him continue. A sickening flood of shame and confusion rushed in to ruin whatever afterglow could have possibly come from this.

He had to leave.  _Now._

It mattered little how much energy it would take. He forced himself to his feet and teleported home without a second thought. There he stumbled and immediately collapsed upon the living room carpet in a dead sleep.

Knocking himself unconscious seemed better than coming to terms with whatever had just happened.  _He could pick up his damned sweatshirt tomorrow._

**Author's Note:**

> Questions? Comments? I'd love to see 'em. :)


End file.
